Much effort has been directed to development of couplings for sealing joints between pipe sections. Many pipe lines must be assembled from a series of pipe sections abutted end-to-end, and require that fluids conveyed the length of the pipeline not leak through the joints. Typically, a coupling for joining two abutting pipe ends fits around the exterior of the pipe and spans the adjacent ends.
An example of such a coupling is shown in U.S. Pat. No. 4,664,428, which discloses the use of an axial gasket along edges of a sealing plate fitted under the axial joint in the pipe coupling, or positioned along an axial edge of the coupling which is spaced under another axial edge of the coupling. Couplings embodying these concepts have been very useful in sealing pipe joints from the outside of the pipes with an apparatus that can be successfully installed by relatively unskilled workers.
Other exterior pipe couplings are shown in U.S. Pat. Nos. 2,913,262 and 3,153,550, which provide an axial gasket member within axial joints of the coupling between o-rings which surround the pipe ends. Another approach shown in U.S. Pat. No. 1,607,943 and in French patent No. 355,620 has been to provide an annular central web connecting the o-rings and completely surrounding the pipe ends. U.S. Pat. No. 4,360,227 discloses a pipe coupling in which a unitary gasket is provided including o-rings for surrounding the pipe ends joined by a web only in the area of the axial slit of the coupling.
Joints in metal pipe lines are often welded, whereas joints in concrete pipe lines often are sealed by o-rings. Installation of exterior couplings to repair such joints can be very inconvenient in the case of leaking joints in buried pipe lines. The pipe joint must be completely excavated to allow repair of leaks, and the heavy equipment typically used for such excavation must not damage the pipe ends. Furthermore, it may be quite difficult to determine the location of a leak along such a pipe line. Thus, there has been a need in the art for a method and a pipe coupling for sealing leaks in pipe lines without providing access to the exterior of the pipe line at the location of the leak. Many pipe lines exist which are large enough to permit access to the interior of the pipe.